There are not enough divisions in Bydgoszcz...
SOV takes eastern Poland only if Warsaw is captured by Germans. Without it, they remain silent. And in all of my games, as long as I remain in the Allies and guarantee independence of baltic states, they let them be.
And one more thing. In my games as Poland I always modify my cores - I remove my claims on Soviet Union (all these territories had Poles only as minority and treaty of Riga border fully satisfid polish authorities), while I add core on Oppeln (it represents the rest of upper Silesia - plebiscite area) and Elbling (similar thing - Warmia, plebiscite, lost only because it was held when Red Army was at the gates of Warsaw).